This project is a minimum working example of deploying a Lambda function accessible through an API Gateway using Python flavored AWS CDK. The API allows you to pass data directly into the Lambda function and get a response back with a result.
For maybe a better way to do this using the new Lambda Function URL
feature recently released by AWS
see my post here.
What is possible using this pattern?
1) Pass data to the function, get a machine learning prediction back.
2) Request a file stored on S3
, get a secure link back.
3) Send parameters to the function, get complex calculations back.
4) Database retrieval.
etc...
The Github repository can be found here.
CDK init & deploy
I won’t cover setting up CDK and bootstrapping the environment. You can find that information here.
Once you have set up CDK, we need to set up the project:
mkdir CDK_Lambda_API && cd CDK_Lambda_API
cdk init --language python
source .venv/bin/activate
Optional: If you need additional libraries in your Lambda function, add
aws-cdk.aws-lambda-python-alpha
to requirements.txt to allow custom builds during stack deployment using Docker.-
pip install -r requirements.txt && pip install -r requirements-dev.txt
Now deploy empty stack to AWS:
cdk deploy
Stack design
This stack will deploy a lambda function using aws-lambda-python-alpha
to build the function with all its additional libraries using a docker container. Make sure to have Docker installed and the daemon running before running cdk deploy
.
# lambda_api_stack.py
from aws_cdk import Stack
from aws_cdk import aws_apigateway as apigw
from aws_cdk import aws_lambda as _lambda
from aws_cdk import aws_lambda_python_alpha as _lambda_python
from constructs import Construct
class LambdaModelPredictionsStack(Stack):
def __init__(self, scope: Construct, construct_id: str, **kwargs) -> None:
super().__init__(scope, construct_id, **kwargs)
# in __init__ I like to initialize the infrastructure I will be creating
self.prediction_lambda = None
self.gateway = None
# Additional useful infrastructure might include an S3 bucket,
# an EFS store, SQS queue, etc.
self.build_infrastructure()
def build_infrastructure(self):
# For convenience, consolidate infrastructure construction
self.build_lambda()
self.build_gateway()
def build_lambda(self):
self.prediction_lambda = _lambda_python.PythonFunction(
scope=self,
id="PredictionLambda",
# entry points to the directory
entry="lambda_funcs/APILambda",
# index is the file name
index="API_lambda.py",
# handler is the function entry point name in the lambda.py file
handler="handler",
runtime=_lambda.Runtime.PYTHON_3_9,
# name of function on AWS
function_name="ExampleAPILambda",
)
def build_gateway(self):
# This will attach an API gateway as a trigger to our
# lambda function above. The return of the handler function also
# gets routed back to the API gateway.
self.gateway = apigw.LambdaRestApi(
self, "Endpoint", handler=self.prediction_lambda
)
Minimum Working Lambda Function
You can see here an example of the response format the API gateway is expecting.
# lambda_funcs/APILambda/API_lambda.py
from logging import getLogger
logger = getLogger()
logger.setLevel(level="DEBUG")
def handler(event, context):
logger.debug(msg=f"Initial event: {event}")
response = {
"isBase64Encoded": False,
"statusCode": 200,
"headers": {
"Access-Control-Allow-Origin": "*",
},
"body": f"Nice! You said {event['queryStringParameters']['q']}",
}
return response
Now you can do cdk deploy
. The lambda function will be built using docker and uploaded to the bootstrapped ECR repository. Once the project is built, it will synth a CloudFormation
template and begin deploying the infrastructure. You can watch your stack deploy on AWS CloudFormation
- it should be quick since the infrastructure is relatively simple.
Once the process is completed, CDK will output the endpoint URL of the API Gateway:
Query the API Gateway
To query the API gateway and get a response back from your lambda function, just send a get request using requests
or Postman
That's all! Make sure to cdk destroy
when you're done to avoid any charges.
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